For various electronic devices or the like such as portable terminals represented by cell phones, various types of batteries are used as the power supply. In addition, exhaust controls of carbon dioxide gas and the like are being tightened in view of the recent moves to protect the environment. In the car industry, not only automobiles using fossil fuels such as gasoline, diesel oil and natural gas, but also electric vehicles (EVs) and hybrid electric vehicles (HEVs) have been developed actively. In addition, a recent sudden rise in the price of the fossil fuels has accelerated the development of EVs and HEVs.
As for secondary batteries used for such applications, nonaqueous electrolyte secondary batteries represented by a lithium ion battery and alkaline storage batteries represented by a nickel-cadmium storage battery, nickel-hydrogen storage battery, and the like are known. Among them, the nonaqueous electrolyte secondary batteries represented by the lithium ion battery have excellent characteristics, for example, high operating voltage (3 V or higher), high theoretical energy density as compared with aqueous solution based batteries, low self-discharge, wide range of operating temperature, and excellent liquid leakage resistance. Consequently, their application has been increasing.
Nonaqueous electrolyte secondary batteries, for example, a cylindrical-shaped battery, are assembled in the following steps: positive and negative electrode plates interposing a separator therebetween are rolled to manufacture a cylindrical-shaped rolled electrode assembly; the cylindrical-shaped rolled electrode assembly is inserted into a cylindrical-shaped battery outer body and a nonaqueous electrolyte is poured; and a mouth of the battery outer body is sealed with a sealing body having a positive or negative electrode terminal to be a sealed-state.
At that time, a roll end of the rolled electrode assembly is fixed with an adhesive tape for fixing a roll end so as not to loosen, and the rolled electrode assembly is inserted into the cylindrical-shaped battery outer can. For example, JP-A-07-320770 discloses an invention relating to batteries including a spirally electrode assembly in which, as Comparative Example 1, a separator of the spirally electrode assembly extends over a roll end of an electrode plate, and only a roll end of the separator is fixed with an insulating tape. Furthermore, JP-A-09-293537 discloses an invention relating to nonaqueous electrolyte secondary batteries in which a separator of a rolled electrode assembly extends over a roll end of an electrode plate, and only a roll end of the separator is fixed with an insulating tape.
In the above nonaqueous electrolyte secondary batteries including the rolled electrode assembly having the positive electrode plate, negative electrode plate, separator and adhesive tape for fixing a roll end, the roll ends of the positive electrode plate and negative electrode plate have steps, so that stress from the inside concentrates on the roll end side when the rolled electrode assembly expands. Furthermore, the outer side of the adhesive tape for fixing a roll end is pressured from the outer can when the rolled electrode assembly expands. Moreover, in charge and discharge cycles at high voltage of the nonaqueous electrolyte secondary battery, oxidation-reduction decomposition of the electrolyte is accelerated, so that the rolled electrode assembly further expands, and then the roll end side of the rolled electrode assembly is readily stressed.
Moreover, recently, as disclosed in JP-A-2008-210573, positive electrode plates capable of being charged at a high voltage of 4.4 V or higher vs. Li have been developed. In the positive electrode plates which are charged and discharged at such high voltage, the nonaqueous electrolyte is violently decomposed to generate a large amount of gas, and consequently, the rolled electrode assembly expands larger to further stress the roll end of the rolled electrode assembly.
In contrast, when an outermost periphery side of the rolled electrode assembly is made to be an exposed portion of the negative electrode substrate where the negative electrode active material mixture layer of the negative electrode is not formed, and then a negative electrode tab is attached to the outermost periphery side of the negative electrode substrate, the negative electrode plate, positive electrode plate, adhesive tape for fixing a roll end and the like necessarily form steps at the roll end of the rolled electrode assembly. Because of this, at worst, the positive electrode plate or negative electrode plate may be broken by the stress from the inside, the pressure from the outer can as well as the repeated expansion and contraction of the rolled electrode assembly accompanied with charging and discharging and the impact, vibration, or the like from the outside.